The Rochester Epidemiology Project (REP) is a unique, population-based data resource comprised of the complete (impatient and outpatient) medical records of all Olmsted County, MN residents for the entire duration of their residency in the County. Our data base now covers the medical care delivered by essentially all providers to County residents from 1909 through the present and has resulted in 565 publications since the system was organized in 1966 (and 212 since the last competitive renewal five years ago) on a myriad of topics--many relating to critical health issues of national importance. The REP supports the work of a large number of investigators from Mayo and other academic institutions in the United States and abroad and makes possible the efficient conduct of extramurally funded studies of coronary heart disease, stroke, dementia and other neurological conditions, cancer, diabetes and other metabolic diseases, gastrointestinal disorders, osteoporosis, arthritis, and other. Although Mayo Clinic contributes substantially by indexing the diagnoses, surgical procedures and pathology recorded in its own records at no cost to this project, it is the responsibility of the REP to collect the diagnostic data from non-Mayo providers, to integrate the information from all sources of care, and to make it accessible to all qualified investigators for descriptive and analytic studies. Continued support is needed to supplement the Mayo Clinic diagnostic index with data from the Olmsted Medical Group, the Olmsted Community Hospital and several other non-Mayo sources of medical care in and around Olmsted County and to undertake organizational tasks that enhance the research capabilities of the Rochester Epidemiology Project and increase its efficiency. The funds requested are required to (1) maintain and continue adding to the non-Mayo portion of the REP data base, which makes possible the full level of case ascertainment and follow-up required for population-based studies in Rochester and Olmsted County and forms the essential core for epidemiologic research in this population; (2) extend our research capabilities by forming new indexes for laboratory results, diagnostic procedures and medications; (3) modernize the data base by using relational data base technology to develop a global file (the REP Medical Profile) containing a longitudinal record of names, identification numbers, residences, episodes of medical care and hospitalization, clinical and pathological diagnoses, surgical and diagnostic procedures, laboratory values, prescription drugs, and linkages to the detailed data of each resident enrolled in a specific study or registry; and (4) enhance the efficiency of logistical support by automating many of the procedures for sample selection, for residency verification, and for generating and tracking follow-up correspondence, and by establishing an interface with the National Death Index.